Title: It's All In Your Head - What Hominid Skulls Tell Us
Lesson Overview
This lesson is meant to show what comparing the skulls of humans and our ancestors can tell us about how we evolved, and why we evolved the way we did. Students will be comparing the features of several species of hominids (including humans) to examine what changes have occurred over millennia.
Objectives
The student will make inferences as to what caused several changing features of the hominid skull. The student will recognize several differing characteristics between earlier hominids and Homo sapiens.
Materials
Science Journals
Hominid Skull Profile Sheets (6 for each group)
Hominid Skull Comparison Exploration Questions (1 per student)
The instructor will begin class with a science journal prompt while attendance is taken and preparations for the lesson are made. The instructor will also check student outlines 16.1 and 16.2 (previously assigned for homework) for completion as a homework grade. The journal prompt will read: "What does a person's skull tell us about the history of their life? In what situations so we use this type of information? How can we apply in information we learn from a human skull to human evolution?" A short class discussion of the prompt will follow. The instructor will use the prompt to springboard into a short video on the process of unearthing hominid fossil remains by Louise Leakey.
Learning Activities
Then the instructor will introduce the learning activity. The instructor will ask, "Why do scientists like Louise Leakey spend so much time digging up and reconstructing fossil remains of hominids? It's because their remains tell us things about how these species lived, and where we came from. You'll now play the part of a paleoanthropologist who aims to discover some of these things." The students will do a short lab session on comparing the characteristics of skulls of different hominids, including the skull of modern humans.
The instructor will give each group of students (approximately 4 students to a group) a set of profile drawings of hominid skulls, starting from Australopithicus afarensis to modern humans, Homo sapiens (6 in all). Each student will get one sheet of exploration questions. The students will discuss the question together and brainstorm the answers to each one. The questions require students to make inferences and form hypotheses as to why the hominid skulls evolved the way they did.
Closing
With approximately 10 to 15 minutes left in the period, the instructor will being the class back together for a discussion of the activity. The instructor will pose the questions in the packet to the class and ask for answers to them from each group. If the following answers are not given by the group, the instructor must make sure to verbalize these answers to the class. Here are the questions and desired answers, in short:
1. Look for the presence of a supraorbital brow ridge on each skull. This is a ridge-like structure that occurs above the orbits of the eye sockets. On which species does it appear most pronounced? Least pronounced? Make a hypothesis as to the purpose of the brow ridge. The ridge is most pronounced on A. afarensis (Lucy) and least pronounced on H. sapiens. The hypothesis of scientists as to why the ridge becomes less prominent has to do with structural reinforcement of the face and front / top of the skull.
2. Look at the angle and size of the jaw on Australopithicus afarensis ("Lucy"). Note the large canine teeth, and the forward angle of the incisors. What happens to these features in the later hominid skulls? The size of the jaw is drastically reduced by the time H. sapiens speciates. The canine teeth also shrink. The angle of the incisors becomes much more vertical. The overall effect is a flattening of the face.
3. In thinking about your answer to #2: Why would there be less need for a robust, strong jaw? (Think about what many animals do with their jaws, compared to what ape species do with their hands) Many animals hold things with their jaws rather than their limbs. As stronger limbs and hands were selected for, the need for a strong jaw was reduced.
4. Take a look at the relative size of the braincase (the area of the skull behind the face that holds the brain). Describe the trend over time. What areas or portions of the braincase enlarge first and which ones enlarge later in the hominids? The braincase extends horizontally backwards at first, then extends vertically upward.
5. The cerebellum is the portion of the brain that deals with motor coordination and balance, located at the base and rear portion of the brain. The frontal lobes of the cerebrum, located at the top and front portion of the brain, deal with higher-order thinking skills, planning, etc. Connect this information to the evolution of the braincase in hominid species that you explored in #4. As hominids began to learn to walk upright, a larger cerebellum was selected for. The cerebellum handles the motor skills and balance necessary to walk upright rather than on all fours. As higher-order thinking and planning began to be selected for, the hominids with more space for their frontal lobe began to be selected for. The skull expanded vertically to make more space for the frontal lobes of the cerebrum.
6. The foramen magnum is a large hole in the skull at the base of the braincase where the spinal cord can connect into the brain. This foramen is located further to the rear of the skull in earlier hominids, and in later hominids it gradually becomes located underneath the skull rather than to the rear. Why would this be the case? In earlier hominids, the posture of the organism was with a stronger lean forward, because all four limbs aided locomotion. It would make sense for the spinal cord to emerge more toward the back of the skull in this case. For modern humans, who walk completely upright, it makes more sense with an upright posture to have the spinal cord emerge from the base of the skull.
Assessment
Formative assessment will be conducted while the instructor conducts the whole-class discussion. The instructor will collect the sheet of exploration questions at the end of class as a method of formative assessment. The instructor will check the questions for their reasoning and completeness, and return them to the students once they are graded.
Homework
None.
Additional Notes
If it is possible to procure actual physical models of these hominid skulls instead of using simple pictures of the skulls in profile, this is preferable. Procuring sets of these skull models is expensive, however, and budgets might not allow for it.
Unit: Human Evolution
Title: It's All In Your Head - What Hominid Skulls Tell Us
Lesson Overview
This lesson is meant to show what comparing the skulls of humans and our ancestors can tell us about how we evolved, and why we evolved the way we did. Students will be comparing the features of several species of hominids (including humans) to examine what changes have occurred over millennia.
Objectives
The student will make inferences as to what caused several changing features of the hominid skull.
The student will recognize several differing characteristics between earlier hominids and Homo sapiens.
Materials
Science JournalsHominid Skull Profile Sheets (6 for each group)
Hominid Skull Comparison Exploration Questions (1 per student)
Links to Resources
Louise Leakey TED Talk: http://www.ted.com/talks/louise_leakey_digs_for_humanity_s_origins.htmlHominid Skull Comparison Exploration Questions
Hominid Skull Profile Sheets (6 in all)
Safety Issues
None.
Instruction
Opening
The instructor will begin class with a science journal prompt while attendance is taken and preparations for the lesson are made. The instructor will also check student outlines 16.1 and 16.2 (previously assigned for homework) for completion as a homework grade. The journal prompt will read: "What does a person's skull tell us about the history of their life? In what situations so we use this type of information? How can we apply in information we learn from a human skull to human evolution?" A short class discussion of the prompt will follow. The instructor will use the prompt to springboard into a short video on the process of unearthing hominid fossil remains by Louise Leakey.
Learning Activities
Then the instructor will introduce the learning activity. The instructor will ask, "Why do scientists like Louise Leakey spend so much time digging up and reconstructing fossil remains of hominids? It's because their remains tell us things about how these species lived, and where we came from. You'll now play the part of a paleoanthropologist who aims to discover some of these things." The students will do a short lab session on comparing the characteristics of skulls of different hominids, including the skull of modern humans.
The instructor will give each group of students (approximately 4 students to a group) a set of profile drawings of hominid skulls, starting from Australopithicus afarensis to modern humans, Homo sapiens (6 in all). Each student will get one sheet of exploration questions. The students will discuss the question together and brainstorm the answers to each one. The questions require students to make inferences and form hypotheses as to why the hominid skulls evolved the way they did.
Closing
With approximately 10 to 15 minutes left in the period, the instructor will being the class back together for a discussion of the activity. The instructor will pose the questions in the packet to the class and ask for answers to them from each group. If the following answers are not given by the group, the instructor must make sure to verbalize these answers to the class. Here are the questions and desired answers, in short:
1. Look for the presence of a supraorbital brow ridge on each skull. This is a ridge-like structure that occurs above the orbits of the eye sockets. On which species does it appear most pronounced? Least pronounced? Make a hypothesis as to the purpose of the brow ridge.
The ridge is most pronounced on A. afarensis (Lucy) and least pronounced on H. sapiens. The hypothesis of scientists as to why the ridge becomes less prominent has to do with structural reinforcement of the face and front / top of the skull.
2. Look at the angle and size of the jaw on Australopithicus afarensis ("Lucy"). Note the large canine teeth, and the forward angle of the incisors. What happens to these features in the later hominid skulls?
The size of the jaw is drastically reduced by the time H. sapiens speciates. The canine teeth also shrink. The angle of the incisors becomes much more vertical. The overall effect is a flattening of the face.
3. In thinking about your answer to #2: Why would there be less need for a robust, strong jaw? (Think about what many animals do with their jaws, compared to what ape species do with their hands)
Many animals hold things with their jaws rather than their limbs. As stronger limbs and hands were selected for, the need for a strong jaw was reduced.
4. Take a look at the relative size of the braincase (the area of the skull behind the face that holds the brain). Describe the trend over time. What areas or portions of the braincase enlarge first and which ones enlarge later in the hominids?
The braincase extends horizontally backwards at first, then extends vertically upward.
5. The cerebellum is the portion of the brain that deals with motor coordination and balance, located at the base and rear portion of the brain. The frontal lobes of the cerebrum, located at the top and front portion of the brain, deal with higher-order thinking skills, planning, etc. Connect this information to the evolution of the braincase in hominid species that you explored in #4.
As hominids began to learn to walk upright, a larger cerebellum was selected for. The cerebellum handles the motor skills and balance necessary to walk upright rather than on all fours. As higher-order thinking and planning began to be selected for, the hominids with more space for their frontal lobe began to be selected for. The skull expanded vertically to make more space for the frontal lobes of the cerebrum.
6. The foramen magnum is a large hole in the skull at the base of the braincase where the spinal cord can connect into the brain. This foramen is located further to the rear of the skull in earlier hominids, and in later hominids it gradually becomes located underneath the skull rather than to the rear. Why would this be the case?
In earlier hominids, the posture of the organism was with a stronger lean forward, because all four limbs aided locomotion. It would make sense for the spinal cord to emerge more toward the back of the skull in this case. For modern humans, who walk completely upright, it makes more sense with an upright posture to have the spinal cord emerge from the base of the skull.
Assessment
Formative assessment will be conducted while the instructor conducts the whole-class discussion. The instructor will collect the sheet of exploration questions at the end of class as a method of formative assessment. The instructor will check the questions for their reasoning and completeness, and return them to the students once they are graded.
Homework
None.Additional Notes
If it is possible to procure actual physical models of these hominid skulls instead of using simple pictures of the skulls in profile, this is preferable. Procuring sets of these skull models is expensive, however, and budgets might not allow for it.